1. Field of the Invention:
The present invention relates to a fuel evaporation rate control system for a direct fuel injection type spark-ignition internal combustion engine.
2. Description of the Related Art:
An extremely high fuel efficiency can be attained by a direct fuel injection type spark-ignition internal combustion engine in which a fuel is directly injected into the cylinder onto the surface of the wall of a combustion chamber formed at the piston top and then the fuel having adhered to the wall is evaporated through heating the wall thereby generating a combustible gas. However, the direct fuel injection type internal combustion engine has drawbacks as mentioned below.
In the direct fuel injection type combustion engine, when engine speeds and engine loads are widely varied, the temperature of the combustion chamber wall to which the fuel adheres also varies widely. As a result, the fuel evaporation rate becomes too high in a range of high engine loads in which the temperature of the combustion chamber wall rises, resulting in an increase in combustion noise, due to too rapid combustion, and requiring increased engine weight to withstand the higher combustion pressure. Also, in a range of low engine loads and low engine speeds, the temperature of the combustion chamber wall drops too low, resulting in delayed combustion and increased volumes of HC and aldehydes in the exhaust gas.
It is known to spray a cooling oil jet onto the back surface of the combustion chamber wall in a diesel engine. Devices for controlling the volume of an oil jet sprayed onto the back surface of a piston are disclosed in Japanese Utility Model Publication SHO No. 59-22097 and Japanese Utility Model Publication SHO No. 59-49719. However, these prior publications disclose no more than devices for controlling the temperature of the piston of a diesel engine to prevent either excessive cooling or knocking. They have no concern with a spark-ignition type engine.